Electron tube and circuit therefor



April 3, 1951 w. E. EVANS, JR

ELECTRON TUBE AND CIRCUIT THEREFOR Filed Feb. 4, 1949 I N VEN TOR. lVi/fiam 5 Evan 5, Jr W A rrozA/svs ll 2 a a 9 n 3 m h h c c N 8 9 3 3 IIII|III|PIIIIII 2w It L? 5 3 II llllllLllll a 3 S B Patented Apr. 3, 1951UNITED STATES PATENT OFFECE Claims. I

This invention relates generally to vacuum tubes of the electron beamtype, and to circuits making use of the same.

In the p-astradio systems have been proposed which make use of twohighfrequency amplifier channels connected in opposed phase relationship toa common antenna output. Each channel is phase modulated in response toa common source of modulating frequency, whereby the resuiting unbalancein the phase relationship between the two channels provides an intensitymodulated output to the antenna. Circuits which have been proposed forsuch systems (sometimes referred to as phase-to-amplitude systems) areunduly complicated, due largely to the type of electron or vacuum tubesemployed for phase modulation.

It is an object of the present invention to provide an electron tubewhich is capable of greatly simplifying systems of the type describedabove,

. and which incorporates in its construction all that is necessary forsecuring simultaneous phase modulation of two high frequency channels:

Another object of the invention is to provide an electron tube of theabove character capable of supplying relatively large output energy fora tube of given size.

Another object of the invention is to provide a new circuit of thephase-to-amplitude type,

making use of my tube, and which is simpler and more effective thanprior available systems. Further objects of the invention will appearfrom the following description in which the preferred embodiment hasbeen set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing: Figure l is a side elevational view of anelectron. tube incorporating the present invention.

Figure 2 is a fragmentary view of the tube shown in Figure 1, but withthe parts rotated through 90.

Figure 3 is a circuit diagram illustrating the tube of Figures 1 and 2incorporated in. a circuit for phase-to-amplitude modulation.

, The electron tube illustrated in Figures 1 and 2 is of the beam type,is provided with an electron gun of the electrostatic lens type forforming an electron beam and for accelerating and focu ing the beam uponcollecting means. The collect n means consists of two extendedcollecting electrodes which are disposed at an angle with respect toeach other, and also inclined with respect to the normal axis of thebeam. Th se collecting electrodes are separated by an additional elementas will be presently explained. In addition the tube is provided with agrid for varying the beam intensity, and

with deflecting electrodes adapted to receive voltages for deflectingthe beam laterally. In place of an'electron gun of the electrostaticlens type, I can employ any other type of gun struccontrol grid IS, theaccelerating anode l4, and

the focusing electrode I 5. Deflecting electrodes IE, which are disposedupon opposite sides of the axis of the beam, can be connected toseparate external'terminals IT. A pair of collecting electrodes I8 areprovided which are in the form of elongated metal strips. Theseelectrodes can be connected to and supported by the external terminalsl9. As illustrated they are planar in form, although in some instancesthey may be formed with a predetermined amount of curvature to obtain adesired nonlinear modulation characteristic.

It will be noted from Figure 1 that the two collecting electrodes I8extend at an angle of substantially with respect to each other, and thateach element is at an angle of substantially 45 with the axis of thetube (which axis corresponds to the normal undefiected axis of theelectron beam) Normally the focusing electrode 15 is so shaped, and ismaintained at such a potential, that the electron beam produced issubstant ally rectangular in transverse cross-sectional contour. Thelength of the cross-sectional contour of the beam in the vicinity of theelectrodes l8 should be ample to insure simultaneous impingement overeoual areas on both of the col ecting electrodes. The width of thiscrosssectional contour should be such that the areaof impingement uponeach collecting electrode at any one instant is a minor fraction of thelength of the electrode. For exa ple where each collecting electrode maybe say 2 inches in length, the extent of impingement may be for the fullwidth of the electrode, and for a distancealong the length of theelectrode of say 0.1 inch.

The electrode 2! which is interposed between the collecting electrodes[8 is normally positively biased. As will be presently explained, inoperation secondary emission occurs from the collecting electrodes 18,and such secondary emission is utilized in conjunction with electrode 2|to remove the physically long electron beam and return path from a highfrequency output circuit, and to obtain some power gain for the output.

Figure 3 illustrates a complete system utilizing the tube of Figures 1and 2. In this system a suitable power supply 26 is shown connected tothe cathode i2, the accelerating electrode Hi and the focusing electrodel5. The focusing electrode can be grounded as illustrated. There is alsoa connection, through the high frequency choke 2'! to the control gridE3, in order to properly bias the same. A source of modulating voltage28 is shown connected to the two deflecting electrodes I6. A highfrequency source .29, such as a pilot oscillator and amplifier, isconnected to supply voltages of a desired carrier frequency to the gridl3, through the coaxial transmission line 3i and the coupling means 32.

The output terminals I? of the tube are shown connected to the coaxialtransmission lines 33.

Y which are adjusted to be resonant to the frequency of the source 29.Thus the effective electrical length of each line is made equal toonequarter wave length. A conductor 35 connects with th terminal 22, andleads to the power" supply 26 or some other source of voltage formaintaining a desired positive bias upon the electrode 2!. A highfrequency by-pass condenser 37 connects between the terminal 22 andground. Coaxial taps 33 are connected to the transmission lines 33, andserve to supply energy to the two high frequency channels 39. Thesechannels may include high frequency electronic amplifying means, andtheir outputs are connected in opposed phase relationship to the commonantenna 4 l which forms an output load.

Assuming that there is no voltage difference between the deflectingelectrodes It, the electron beam impinges upon the middle portions ofthe two collecting electrodes I8. High frequency voltages applied to thecontrol grid 53 from the source 29 (for example at a frequency with arange of say from 100 to 300 megacycles), cause intensity modulation ofthe electron beam, with the result that the collecting electrodes l3supply high frequency energy to the resonant transmission lines 33, andfrom thence to the channels 39. For this condition the phaserelationship between the outputs of the two channels 39 can be such (asfor example about 135) that the resultant output to the antenna llcorresponds to carrier level. Assuming now that a voltage difference isapplied to the electrodes Iii from the modulating source 28, theelectron beam will be deflected (upwardly or downwardly as the tubeviewed in Figure l) and as a result one portion of the beam whichimpinges upon one collecting electrode I8 is effectively shortened,whereas the other portion of the beam which impinges the othercollecting electrode is effectively lengthened. This results in 2.corresponding shift in the phase relationship of the high frequencyenergy supplied to the two resonant transmission lines 33. Positivemodulation serves to bring the two channels more in phase to produce thepeaks of modulation, and negative modulation brings the two channelsmore out of phase, thus reducing the output for producing the modulationtroughs. In a typical instance the modulating voltages applied to thedeflecting electrodes it will be of video frequency in order to secureamplitude modulation or a television transmitter.

The energy output from the collecting elec trodes I8 is relatively greatdue to the effect of secondary emission. Thus as a result of impingementof primary electrons upon the electrodes i8, secondary emission occurs,thus causing current flow to occur between each collecting electrode andthe intermediate associated electrode 2:. By the use of secondaryemission in this fashion a tube of given size will have a relativelyhigh power gain, thus greatly simplifying the design of the tube, andalso the design of the amplifying channels 39 and other parts of theelectrical. system with which the tube is used.

I claim:

1. In a vacuum tube, means for forming an electron beam, a pair ofcollecting electrodes oppositely inclined to the normal axis of the beamand adapted to collect electrons from the same, said beam beingproportioned to form two adiacent beam sections for impingement on thoseportions of both the collecting electrodes which are in the path of thebeam at any one instant,

' a control grid for controlling the intensity of the beam in accordancewith the frequency of voltages applied to the same, and means forcausing lateral deflection of the beam to thereby oppositely vary thephase relationship between the frequency of voltages applied to thecontrol electrode and voltages assumed by the collecting electrodes.

2. In a vacuum tube, means for forming an electron beam, a pair ofcollecting electrodes oppositely inclined to the normal axis of thebeam, said beam being proportioned to form two adjacent beam sectionsfor impingement on those portions of both the collecting electrodeswhich are in the path of the beam at any one instant, a metal elementadapted to be positively biased and disposed between the collectingelectrodes and parallel to the normal axis of the beam, a control gridfor controlling the intensity of the beam, and means for effectinglateral deflection of the beam to thereby oppositely vary the phaserelationship between the frequency of voltages applied to the controlgrid and voltages assumed by the two collecting electrodes.

3. In a vacuum tube, means for forming a beam of electrons, a pair ofcollecting electrodes onpositely inclined to the normal axis of thebeam, said beam being proportioned to form two adiacent beam sectionsfor impingement on those portions of both the collecting electrodeswhich are in the path of the beam at any one instant,

a metal shied being disposed between the collecting electrodes with itsplane para lel to the normal axis of the beam, a control grid for controling the intensity of the beam, said sh eld being adapted to be ositivey biased and said collectin electrodes being capable of secondary emision, and means for efiecting lateral defl ction of the beam in a planeparallel to said shield.

4. In an. electronic system employing phaseto-inten -ity modul t on, avacuum tube, said vacuum tube including means forming an electron beam,a pair of collecting electrodes oppositely inclined to the normal ax sof the beam and adapted to collect electrons from the same,

beam being proportioned to form two adjacent beam sections forimpingement on those portions of both the collecting electrodes whichare in the path of the beam at any one instant, a control grid forcontrolling the intens ty of the beam in accordance with voltagesapplied to the frequency energy coupled to apply voltages to the controlgrid, a pair of output channels coupled to the collecting electrodes, anoutput load, the outputs of said channels being connected in opposedphase relationship to the load, and means for applying modulatingvoltages to the deflecting electrodes, whereby deflection of the beamresponsive to said modulating voltages causes changes in phaserelationship between said channels to efiect intensity modulation ofhigh frequency energy supplied to the load. I

5. In an electronic system employing phaseto-amplitude modulation, avacuum tube comprising means forming an electron beam, a pair ofcollectin electrodes oppositely inclined to the normal axis of the beam,said beam being proportioned to form two adjacent beam sections forimpingement on those portions of both the collecting electrodes whichare in the path of the beam at any one instant, a metal shield disposedbetween the collecting electrodes with its plane parallel to the normalaxis of the beam, said shield being interposed between two adjacentsections of the beam which impinge upon the collecting electrodes, acontrol grid for controlling the intensity of the beam, and deflectingelectrodes for effecting lateral deflection of the beam in a planeparallel to said shield, a source of high frequency energy coupled tothe control grid to efi'ect high frequency-intensity modulation of thebeam, a source of modulatin voltage coupled to the deflecting electrodeswhereby the beam is deflected laterally in ac-' the load of an intensitydependent'upon the magnitude of the modulating voltages,

WILLIAM E. EVANS, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,165,308 Skellett July 11, 19392,265,145 Clarke Dec. 9, 1941 2,274,194 Farnsworth Feb. 24, 1942

